Liquid crystal beam control device with improved zone transition and method of manufacture thereof

ABSTRACT

A liquid crystal optical device is described configured to provide variable beam steering or refractive Fresnel lens control over light passing through an aperture of the device. The device includes at least one layer of liquid crystal material contained by substrates having alignment layers. An arrangement of electrodes is configured to provide a spatially varying electric field distribution within a number of zones within the liquid crystal layer. The liquid crystal optical device is structured to provide a spatial variation in optical phase delay with a transition at a boundary between zones which is an approximation of a sawtooth waveform across the boundaries of multiple zones. The arrangement of electrodes, device layered geometry and methods of driving the electrodes increase the effective aperture of the overall optical device.

RELATED APPLICATIONS

This application is an internationally filed non-provisional applicationof, and claims priority from, U.S. Provisional Patent Application62/083,665 filed Nov. 24, 2014 and U.S. Provisional Patent Application62/216,951 filed Sep. 10, 2015, the entireties of which are incorporatedherein by reference.

TECHNICAL FIELD

This disclosure relates to liquid crystal optical devices, such aslenses and beam steering devices, which have neighboring segments orzones, and their manufacturing.

BACKGROUND

It has been proposed to make beam steering devices and Fresnel lensesusing nematic liquid crystal cells that are dynamically controlled by acontrol electric field and have separated element zones. These deviceshave spatial variations in the index of refraction due to the spatialvariations in liquid crystal molecular orientation. This creates aspatial variation in the optical phase delay that can provide beamsteering devices and Fresnel lenses. Liquid crystal beam control devicesare known in the art.

Such devices typically use patterned electrodes over a liquid crystalcell to create a spatial variation in the index of refraction that isuseful to control a beam. To keep voltages low, electrodes can be placedon the cell substrates on the inner side or sides. To increase opticalperformance, the size or aspect ratio of beam shaping elements definedby the patterned electrodes can be small. To provide a device with alarge aperture, many beam steering elements are arranged together, muchlike a Fresnel lens or beam steering device. With liquid crystal beamsteering devices, the boundaries between adjacent beam steering elementscan take up a large portion of the aperture, for example up to 50%,because the liquid crystal orientation changes by almost 90 degrees fromone side of the boundaries to the other.

Unlike physical (fixed) Fresnel lenses or beam steering devices wherethere can be an abrupt change in the refractive properties at theboundary between different sections (herein referred to as “microelements” with the understanding that the sections or micro elements arenot necessary limited to very small dimensions), in the case of anelectric field control over the orientation of liquid crystal molecules,it is difficult to have an electric field that can cause an abruptchange in the orientation of the liquid crystal molecules. This resultsin a substantial portion of the aperture of the optical device not beingable to contribute to the desired optical operation of the device. Thisportion can be termed a “fly-back” portion or a non-linear zone (NLZ).

Various problems also exist, including the extent of the angularcontrol, the quality of the beam intensity distribution, cost ofmanufacture, voltage of operation, etc. When the boundaries between theneighboring micro elements are not properly controlled, the usefulportion of the optical device is reduced by boundary areas of improperlycontrolled liquid crystal.

SUMMARY

Applicant has discovered a number of characteristics related to theoptical performance of beam steering liquid crystal devices.

Applicant proposes a liquid crystal optical device that provides aspatial variation in the optical phase delay with an abrupt transitionat a boundary between micro elements that is not possible withconventional liquid crystal optical device electric control fieldelectrode systems. This phase delay profile can be an approximation of asawtooth waveform across the boundaries of multiple micro elements. Thephase delay profile need not be a sawtooth waveform over the aperture,however, a spatially compressed or abrupt change in phase delay at theboundary region, similar to that of a sawtooth waveform, is desirable.Applicant also proposes a liquid crystal optical device that improvesthe electric field control of liquid crystal at the boundary betweenmicro elements. This reduces improperly steered (redirected) or focussedlight, and it also increases the effective aperture of the opticaldevice.

The improved phase delay transition at the boundary between microelements can be achieved using a combination of low and high frequencyelectric fields with a dual frequency liquid crystal.

The improved phase delay transition at the boundary between microelements can be achieved using floating electrodes that help to shapethe electric field within the micro elements.

The improved phase delay transition at the boundary between lens and/orsteering elements can be achieved using a pair of liquid crystal layerseach having micro elements separated by optically inert zones thatcorrespond to optically inert zones and micro elements of the otherlayer, so that the electric field acting on the liquid crystal of themicro elements does not act on the inert zones.

The improved phase delay transition at the boundary between lenselements can be achieved using a conductive wall arranged between liquidcrystal micro elements, so that the electric field acting on the liquidcrystal of one micro element does not act on the liquid crystal ofneighboring micro elements.

The improved phase delay transition at the boundary between lens and/orsteering elements can be achieved using a difference in the phase ofelectrical signals supplied to the electrodes of the liquid crystalmicro elements, so that the electric field acting on the liquid crystalof one micro element is directed in part in a direction of the liquidcrystal layer direction, with the result also that the electric fieldsgenerated by electrodes from neighboring micro elements have a minimalinfluence of the phase delay profile. Differences in voltage of themicro element electrodes can also be used to achieve the desiredelectric field and liquid crystal control interaction.

Applicant has discovered that an electric field profile suitable forbeam steering, namely type of sawtooth profile, can be achieved using anoffset between a strip electrode on one side of the liquid crystal celland a wider middle electrode on an opposed side of the liquid crystalcell. The result of this electrode geometry is to provide an intenseelectric field in the liquid crystal cell near the strip electrode and agradually decreasing electric field in the liquid crystal cell extendingacross the middle electrode. The offset provides an electric fieldformation with field lines extending from the strip electrodeessentially perpendicularly through the cell to wrap around the oppositeside of the middle electrode. The lines of electric field are quiteperpendicular through the liquid crystal for an electrode arrangementthat does not use a weakly conductive layer or a great distance betweenthe opposed electrodes.

This electrode arrangement provides a beam steering liquid crystalprofile when there is no effective electrode on the opposed side of theliquid crystal cell to the side of the strip electrode opposite wherethe wider middle electrode is located. To provide beam steering over thewhole aperture, two layers of liquid crystal can be arranged to have thespaced apart beam steering liquid crystal elements of one layer alignedwith the idle or non-beam steering liquid crystal elements of the otherlayer.

The direction of steering can be changed by using additional middleelectrodes (so that the beam steering liquid crystal orientation profileform in the other direction) or by using additional strip electrodesprovided on the other side of the middle opposed electrodes.

Applicant has also discovered that such an offset electrode structurecan provide a good effective aperture for a beam steering device havinga single layer by using time multiplexed control of the electrodes. Thuswhen electrodes of odd elements are powered, the electrodes of evenelements can be disconnected to be electrically floating, and when theelectrodes of even elements are powered, the electrodes of the oddelements can be disconnected to be electrically floating.

Applicant has also discovered that the optical performance of the devicecan be dependent on the direction of light travel through the device,for example from top to bottom versus from bottom to top, when theelectric field is different between near one substrate and near theother substrate of the liquid crystal cell. The difference due to thedirection of travel through the device can be very significant forcertain geometries or designs of devices.

Applicant has also discovered that different direction (e.g. orthogonal)patterned electrode arrays can be arranged with separation by a thininsulating layer on a common substrate and provide dual direction beamcontrol using a single layer of liquid crystal (for the polarizationcontrolled by the layer). Such a device can provide beam controlindependently in each of the directions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by way of the following detaileddescription of proposed embodiments with reference to the appendeddrawings, in which:

FIG. 1 is a schematic sectional diagram of a portion of a prior artliquid crystal beam steering device having two zones or beam steeringmicro elements, in which control of the electric field is achieved by alarge number of electrodes to provide a spatially variable electricfield;

FIG. 2 is a schematic sectional diagram of a portion of a prior artliquid crystal beam steering device having two zones or beam steeringmicro elements, in which control of the electric field is achieved bytwo electrodes per zone and a layer of a highly resistive material tohelp extend the electric field across each zone;

FIG. 3 is a schematic sectional diagram of a dual frequency liquidcrystal (DFLC) beam steering device having two zones or beam steeringelements, in which control of the electric field is achieved by twoelectrodes per zone and a layer of a highly resistive material tocontrol the extent of the electric field across each zone, in which anelectrode is supplied a high frequency electrical signal causing localalignment of the liquid crystal perpendicularly to an non-localalignment of liquid crystal with the electric field at lowerfrequencies;

FIG. 4 is a graph of simulated liquid crystal orientation induced phasedelay as a function of distance between electrodes for the embodiment ofFIGS. 2 and 3, showing the non-linear zones (NLZ) for the two cases;

FIG. 5 is a schematic sectional diagram similar to FIG. 3 in which eachzone has two electrode strips at frequency f1;

FIG. 6 is a schematic diagram of the device of FIG. 5 shown in plan viewwith five zones and connected to a driver circuit;

FIG. 7A is a schematic cross-sectional diagram across neighboring zonesor beam steering elements of a LC beam steering device, in which controlof the electric field is provided by two control electrodes per zoneemploying a conductive wall in the transition zone, in accordance withthe proposed solution;

FIG. 7B is a schematic cross-sectional diagram across neighboring zonesor beam steering elements of a LC beam steering device for FIG. 7A, inwhich control of the electric field enhanced by the use of a layer of aweakly conductive material to help extend the electric field across eachzone, in accordance with the proposed solution;

FIG. 7C is a schematic cross-sectional diagram illustrating another LCbeam steering device as illustrated in FIG. 7B having an electricallyfloating electrode, in accordance with another embodiment of theproposed solution;

FIG. 8A is a schematic cross-sectional diagram across neighboring zonesor beam steering elements of a LC beam steering device, in which controlof the electric field is provided by one control electrode per zoneemploying wide optically transparent walls extending in every otherelement zone, in accordance with the proposed solution;

FIG. 8B is a schematic cross-sectional diagram across neighboring zonesor beam steering elements of a LC beam steering device for FIG. 8A, inwhich control of the electric field enhanced by the use of a layer of aweakly conductive material to help extend the electric field across eachzone, in accordance with the proposed solution;

FIG. 8C is a schematic cross-sectional diagram illustrating another LCbeam steering device as illustrated in FIG. 8B having an electricallyfloating electrode, in accordance with another embodiment of theproposed solution;

FIG. 9A is a schematic cross-sectional diagram across neighboring zonesor beam steering elements of a dual LC layer beam steering device, inwhich control of the electric field is provided by one control electrodeper zone employing staggered wide optically transparent walls in everyother element zone, in accordance with the proposed solution;

FIG. 9B is a schematic cross-sectional diagram across neighboring zonesor beam steering elements of a LC beam steering device for FIG. 9A, inwhich control of the electric field enhanced by the use of a layer of aweakly conductive material to help extend the electric field across eachzone, in accordance with the proposed solution;

FIG. 9C is a schematic cross-sectional diagram illustrating another LCbeam steering device as illustrated in FIG. 9B having an electricallyfloating electrode, in accordance with another embodiment of theproposed solution;

FIG. 10A is a schematic cross-sectional diagram across a single zone orbeam steering element of a LC beam steering device having two activeelectrodes driven by drive signal components of same frequency, phaseand amplitude in a non-steering state, in accordance with an embodimentof the proposed solution;

FIG. 10B is a schematic cross-sectional diagram across a single zone orbeam steering element of a LC beam steering device of FIG. 10A whereinthe two active electrodes are driven by drive signal components of samefrequency and phase but opposing amplitude, in accordance with anembodiment of the proposed solution;

FIG. 10C is a schematic cross-sectional diagram across a single zone orbeam steering element of a LC beam steering device of FIG. 10A whereinthe two active electrodes are driven by drive signal components of samefrequency and phase but different opposing amplitudes, in accordancewith an embodiment of the proposed solution;

FIG. 11 is a schematic cross-section illustration of a beam steeringoptical device having a patterned electrode with four beam shapingelements within a liquid crystal cell in which strip electrodes are onone substrate and a planar electrode is on an opposed substrate of thecell, in accordance with an embodiment of the proposed solution;

FIG. 12 is a schematic cross-section illustration of a beam steeringoptical device having four beam shaping elements within a liquid crystalcell in which strip electrodes are on one substrate of the cell to forman in-plane and fringe electric field between the electrodes, inaccordance with an embodiment of the proposed solution;

FIG. 13A is an enlarged view of a variant of one element of the cell ofFIG. 12 in which the aspect ratio of strip electrode gap to cell gapthickness is large, in accordance with an embodiment of the proposedsolution;

FIG. 13B is an enlarged view of a variant of one element of the cell ofFIG. 12 in which the aspect ratio of strip electrode gap to cell gapthickness is small, in accordance with an embodiment of the proposedsolution;

FIG. 13C is an enlarged view of one element of the cell of FIG. 12, inaccordance with an embodiment of the proposed solution;

FIG. 14 is a schematic plan view of an element according to FIG. 13C inwhich liquid crystal alignment is parallel to the strip electrodes, inaccordance with an embodiment of the proposed solution;

FIG. 15A is a schematic representation of a cross-section of a liquidcrystal beam steering device having two liquid crystal cells, poweredstrip electrodes on one substrate and offset middle electrodes that aregrounded, with odd elements of the upper cell having middle electrodesand even elements having no middle electrodes, and even elements of thelower cell having middle electrodes and odd elements having no middleelectrodes, in accordance with an embodiment of the proposed solution;

FIG. 15B shows a variant of FIG. 15A in which the offset is such thatthe middle electrode extends out and the strip electrodes are inset, inaccordance with an embodiment of the proposed solution;

FIG. 16 is an illustration of electric field lines and liquid crystalreorientation derived from simulation for the embodiment of FIG. 15A, inaccordance with an embodiment of the proposed solution;

FIG. 17 is an illustration of simulation results for optical phase delayas a function of position across the device of FIG. 15A, in accordancewith an embodiment of the proposed solution;

FIG. 18A is a schematic cross-section illustration of a single liquidcrystal cell beam steering device that can be operated in a timemultiplexed manner to provide a beam steering optical phase delayprofile in each element of the device (namely both odd and even), shownin the state of actuation of odd elements, in accordance with anembodiment of the proposed solution;

FIG. 18B is the same illustration as FIG. 18A, shown in the state ofactuation of even element, in accordance with an embodiment of theproposed solution;

FIG. 19 illustrates simulation results for the configurations of FIGS.18A and 18B, in accordance with an embodiment of the proposed solution;

FIG. 20 is a schematic plan view of an array of strip electrodes havinga spatially variable gap or spacing between the strip electrodes, inaccordance with an embodiment of the proposed solution; and

FIG. 21 is a schematic cross-sectional diagram illustrating in alignmentby the optical axis:

-   -   at the top, a cross-section a conventional refractive Fresnel        lens;    -   in the middle, a cross-section of an optical device geometry,        optically corresponding to the conventional refractive Fresnel        lens, including four stacked LC layers to reduce sensitivity or        image aberrations of the device to incident light that is not        parallel to the optical axis of the overall device as the light        passes through the overall device; and    -   at the bottom, a schematic diagram illustrating a plan view of        the LC lens shown in the middle having a circular geometry        including a central circular micro element and four concentric        band micro elements, in accordance with the proposed solution;        and

FIG. 22 is a schematic plan view of the device illustrated in FIG. 21,in accordance with the proposed solution,

wherein similar features bear similar labels throughout the drawings.While the layer sequence described is of significance, reference to“top” and “bottom” qualifiers in the present specification is madesolely with reference to the orientation of the drawings as presented inthe application and do not imply any absolute spatial orientation.

DETAILED DESCRIPTION Cross-Plane Field Control

FIG. 1 illustrates a beam steering liquid crystal device 10 having twozones or segments 12 a and 12 b. The liquid crystal material iscontained by substrates providing the aperture and being sealed at theiredges (not shown). The electric field is provided by narrow electrodes14 a (for example arranged as strips, as shown in FIG. 6) that are eachsupplied with a desired voltage and are opposite a planar electrode 15.In the embodiment shown, the electrodes are provided on the substratesinside the cell. This can reduce the required voltages, while it ispossible to arrange electrode on the outside of the cell, for example onthe opposite sides of the relatively thin substrates.

As is known in the art, electrodes for a transmissive liquid crystaldevice can be transparent, for example of a coating of indium tin oxide(ITO) material. The approximate voltage as shown (in the inset at thetop of the figure) ramps up at one side of zone 12 a from zero or aminimum value and begins again the same ramp on the other side of thezone boundary in zone 12 b. The drive frequency can be the same for allof the electrodes 14 a, and the liquid crystal molecules 4 orientthemselves to be parallel to the electric field 3. While the drivesignal for a liquid crystal cell is typically an AC signal, in somecircumstances, it will be appreciated that low voltage DC signals canalso be applied.

An alignment layer on the cell walls (not shown) keeps the ground-statenematic liquid crystal molecules aligned in one direction asillustrated. Such alignment layers (such as rubbed polyimide) are wellknown in the art.

The width of the zones 12 is ‘w’, the beam steering angle θ of the zoneis increased by the value of the change in index of refraction δn of theliquid crystal material on opposite extremes of the zone 12 and thethickness of the cell L, however it is reduced as the width ‘w’increases, namely

$\theta \approx {\frac{\delta \; {n \cdot L}}{w}.}$

Therefore, it is desirable to reduce w.

Electric field lines extend from areas of voltage differentials, and theintensity of the electric field drops with the distance between thoseareas. The electric field lines (corresponding to the above describedramps) are schematically illustrated in FIG. 1 in dashed lines ofdifferent weight corresponding to different field strength. When thevoltage applied to the electrode segments 14 a is equal and the planarelectrode 15 is at a common or ground voltage, then the electric fieldin the cell is essentially uniform (no voltage ramps) with electricfield lines being essentially perpendicular to the cell wall substrates(not shown). The field strength is proportional to the voltage dividedby the distance between electrodes 14 a and 15, or the cell gap size.

When the voltage is ramped using small segments 14 a, the electric fieldintensity will be varying spatially across the aperture (for example asschematically illustrated). An electric field that is spatially varying,however with parallel lines all being perpendicular to the substratesover the whole aperture is desirable for control of the liquid crystal.

If some of the segments 14 a were not connected to a potential, theelectric field lines opposite those disconnected segments 14 a would becurved and would reduce in intensity with the distance away from theother powered electrode segments 14 a. Such curved electric field linesare also known as the fringing electric field.

The zero or minimum voltage electrode segment 14 a of zone 12 b has afringing electric field created by the neighboring maximum voltageelectrode segment 14 a of zone 12 a by creating some field lines betweenthe two electrodes 14 a at the zone boundary (there is still an electricfield created by the maximum voltage electrode segment 14 a of zone 12 awithin the cell opposite the zero or minimum voltage electrode segment14 a of zone 12 b). This is schematically illustrated by the arcuatedotted lines between electrode segments between zone 12 a and 12 b inthe central part of FIG. 1. Thus, the desired zero or minimum electricfield in zone 12 b is not achieved. Furthermore, electric field linesare not parallel within the cell opposite the zero or minimum voltageelectrode segment 14 a of zone 12 b, thus leading to undesiredorientation of the liquid crystal molecules between zones 12 a and 12 b.

In the transition area between the zones 12 a and 12 b, a non-linearorientation zone (NLZ) is thus created where the electric field changesfrom being defined by V max down to a field defined by zero or V min. Anabrupt change in the electric field is not possible using suchelectrodes alone. The NLZ can also be called a reset zone or a “fly-backregion”.

The result is that the effective working portion of the device (withlinear ramp) is reduced to the fraction (w-NLZ)/w when many zones 12 areprovided across the aperture of such a device. The NLZ deviates thelight in undesired directions (compared to the linear ramp area thatre-directs light in the desired direction) and is thus not desirable.

In FIG. 2, the series of electrode segments 14 a is simplified by usinga weakly conductive (or highly resistive) layer 16 and a pair ofboundary electrodes 14 b and 14 c. The weakly conductive layer helps togradually spread the voltage across the aperture of each zone 12 a and12 b without requiring a series of individually controlled electrodes 14a, as schematically illustrated using dashed lines in FIG. 2. Thespreading out of the voltage can be controlled using the frequency ofthe voltage applied to electrodes 14 c to shape the voltagedistribution, however this frequency still causes parallel alignment ofthe liquid crystal molecules with the electric field (when thedielectric anisotropy of the LC is positive). Electrodes 14 b can begrounded or connected to a lower voltage level as desired. In thearrangement of FIG. 2, the number of electrodes per zone is reduced fromthe many of FIG. 1 to only two. It is possible to include one or a smallnumber of additional electrodes to help shape the voltage distributionover the aperture, in particular near the edges.

The electric field created using such a hole-patterned electrodearrangement with a weakly conductive layer has lines essentiallyparallel to each other and perpendicular to the substrates over theaperture of the device, and thus is suitable for controlling the liquidcrystal. The expression “hole-patterned electrode” is used to mean whenan electrode structure uses the absence of electrode to create a spatialvariation in the resulting electric field, whether the hole is a gapbetween two independent electrodes, a gap extending beyond an electrode,or an aperture in a single electrode.

It will be understood that the NLZ here (in FIG. 2) is essentially stilla problem as in FIG. 1 while the control electrode complexity has beenreduced i.e. fewer electrodes 14 need to be driven per zone 12.

In FIG. 3, electrode 14 d is provided and connected to a high frequency(illustrated as f2) voltage that acts on the liquid crystal to causeorientation perpendicularly to the electric field. The liquid crystal isa Dual Frequency Liquid Crystal (DFLC), as is known in the art. Withelectrode 14 c connected to a relatively low frequency (illustrated asf1) the electrode arrangement causes orientation of the liquid crystalmolecules parallel to the electric field, the liquid crystal within thecell is oriented by electrode 14 c to be nearly orthogonal to thealignment layers, while the higher frequency provided to electrode 14 dhelps to force the liquid crystal molecules within the cell to beperpendicular to the electric field, and thus to stay parallel to thealignment layers. Because the frequency of the voltage applied to theelectrodes 14 d is high, the weakly conductive layer does not help tospread out the high frequency electric field as much as for the lowerfrequency applied to the electrodes 14 c. The opposite situation mayalso be considered if the ground state alignment of the LC is different,for example, perpendicular to the alignment layers.

The electric field lines schematically illustrated in FIG. 3 as solidfor f1 and dashed for f2. The two fields overlap and their effect isstill felt on the liquid crystal material. Electrode 14 c generates arelatively largely spread electric field that attempts to align theliquid crystal molecules parallel to the field at f1, while electrode 14d generates a relatively localized electric field that attempts toorient the liquid crystal molecules perpendicularly to the electricfield at f2. The fields from the electrodes 14 c and 14 d overlap asillustrated, however the liquid crystal molecules between electrodes 14c and 14 d and electrode 15 are oriented as shown with a spatiallycompressed transition from substantially parallel orientation tosubstantially perpendicular orientation.

An example of a suitable frequency for f1 can be in the range of 1 kHzto 15 kHz depending on the properties of the layer 16 and the geometryof the LC cell. An example of a suitable frequency for f2 is typicallyabove 30 kHz, for example 50 kHz, depending on the properties of theDFLC material and the temperature of operation.

The net effect is to have electric fields at different frequencies thatoverlap, while their effect on the liquid crystal molecules is to causethe rapid change (both in time and space) in liquid crystal orientationat the boundary with a resulting compression in the NLZ as illustrated.In the simulation of FIG. 4, the parameters used are: liquid crystallayer 60 μm thick using MLC-2048 liquid crystal (a DFLC material fromMerck), period of repeated beam steering cells of 150 μm, electrodewidth of 10 μm, gap between electrodes 14 d and 14 c of 10 μm, appliedvoltage of 10V at frequency f1 of between 5 kHz and 10 kHz with avoltage of 5.5 V at frequency f2 of 100 kHz. The vertical axis is thephase delay (in microns) of light traversing the LC cell.

The effect of this high frequency field is to cause the liquid crystalto orient in the direction perpendicular to the electric field. Thecombined effect of the control electrode 14 d and the electrode 14 cthat provides the lower frequency electric field in the case of FIG. 3causes the net orientation of the liquid crystal to be more at the peakthan for the other cases of FIGS. 1 and 2, for which the controlelectrode 14 d was simulated as being connected to 0V. However, theshape of the phase delay profile is greatly improved in that the NLZ issubstantially reduced. One can see also that the minimum phase delay isalso reduced for the case of FIG. 3, thus providing a variation in phasedelay for FIG. 3 that is almost as great as for the simulationscorresponding to the embodiments of FIGS. 1 and 2 using the same drivingvoltage for f1. The shape of the phase delay profile for the FIG. 3 caseis also more linearly sloped (closer to an ideal sawtooth waveform) withless of a sinusoidal behavior.

It will be appreciated that the compression of the NLZ achieved for theembodiment of FIG. 3 can be obtained using the multiple segmentedelectrode system of FIG. 1, wherein the first electrode 14 a of zone 12b would be driven with the high frequency voltage that would cause theliquid crystal to orient perpendicularly to the electric field.

In the embodiment of FIG. 5, the (non-circular) hole-patterned (linearpairs of) electrodes of the zones 12 a and 12 b comprise electrodes 14 band 14 c connected to min and max drive voltages at frequency f1.Electrode 14 d connected to a drive voltage at frequency f2 is thenpositioned between electrodes 14 c and 14 b at the boundary betweenzones 12 a and 12 b. This provides better control over the spatialprofile of the resulting (total) dielectric torque, and thus of theliquid crystal orientation. As will be appreciated, if a beam steeringdevice is used to variably steer light in both directions, it isdesirable to drive 14 b with a maximum voltage and 14 c with a minimumvoltage when the steering is in the opposite direction (describedpreviously). It will be appreciated that while separate electrodes 14 cand 14 d are provided to which the low and high frequencies areconnected, the desired phase delay spatial profile can still be achievedusing a single electrode supplied with both frequencies.

The liquid crystal device 10 schematically illustrated in FIGS. 1through 5 comprises a single layer of liquid crystal aligned in onedirection. As is known in the art, such a device acts on a single linearpolarization of light, and unpolarized light passing through the device10 is processed by the device as two linear polarization states. Thespatial modulation of the index of refraction in the liquid crystalmaterial is with respect to one polarization of light, while the otherpolarization has no spatial modulation of the index of refraction. Tohave such a device 10 work with unpolarized light, a second cell istypically provided with LC molecules oriented orthogonally to the LCmolecules of the first cell illustrated in the FIGS. 1 to 5 to act onthe other polarization. Electrodes 14 and 15 are provided for theadditional cell in a manner similar to the first cell.

It is also known from international patent application publicationWO2009/146530 published 10 Dec. 2009 to arrange four cells together,with alignment layers of two cells acting on the same polarizationdirection being in opposite directions. Such an arrangement reduces thesensitivity or image aberrations of the device 10 to light that is notparallel to the optical axis of the device as the light passes throughthe device.

FIG. 6 illustrates a schematic plan view of a beam steering deviceshowing zones 12 a, 12 b, 12 c, 12 d and 12 e that together create anaperture 18. The arrangement of the electrodes 14 b, 14 c and 14 daccording to the arrangement of FIG. 5 is schematically illustrated withthe electrodes connected to a suitable drive circuit 20.

Given the typical dimensions of a liquid crystal cell, namely a cell gapbetween substrates of about 120 microns, and a Δn of about 0.2, it wouldbe desirable to have a zone width in a device as illustratedschematically in FIG. 6 of about 100 microns to provide a beam steeringrange of about +/−13 degrees. If the aperture 18 of the device is to be3 mm across, then there would be 30 zones 12 arranged instead of thefive that are schematically illustrated in FIG. 6.

The drive circuitry for such a device can be done using dedicatedcircuitry, FPGA devices, DSP devices and can include a programmedprocessor for control. As schematically illustrated, the drive circuitry20 has driver 22 operating at frequency f1 for the left electrodes 14 b,a driver 24 operating a frequency f1 for the right electrodes 14 c and adriver 26 operating at frequency f2 for electrodes 14 c. Not shown inFIG. 6 is that the driver circuit 20 is also connected to thecorresponding planar electrode 15. Such drivers 22, 24, 26 can becontrollable to be simply on or off, or they can be variably adjustableto control the variably controllable optical parameter, namely the beamsteering angle. The drivers 22, 24 can also be frequency tunable and/orvoltage tunable. The driver 26 can be fixed in voltage and frequency,although control over its drive signal parameters is also possible. Acontroller 28 is provided as part of the driver circuitry 20 in theembodiment of FIG. 6 to provide the settings of the drivers 22, 24, 26in response to an external control signal input. Such a controller 28can be provided separately from the drivers 22, 24, 26, for example insoftware. The controller 28 typically has stored calibration data toallow a control signal to be translated into specific driver signalvalues. Phase delay control between control signals can also beimplemented for example as described herein with reference to FIGS. 10A,10B and 10C.

While FIG. 6 illustrates a beam steering device that shifts light fromright to left (or vice versa, in the same plane), it will be appreciatedthat by stacking additional cells with electrodes arranged orthogonally,the beam steering device can steer light in two directions, namelyleft-right and up-down.

In accordance with another embodiment of the proposed solution, FIG. 7Aillustrates neighboring zones 12 or beam steering elements 12 of a LCbeam steering device 10, in which control of the electric field isprovided by two control electrodes 14 c and 14 b per zone 12 employing aconductive wall 17 in the transition zone to reduce the fringing fieldof each element 12 from penetrating into the next zone and which formsthe NLZ. Conductive walls 17 can be shorted to planar electrode 15. Tosteer in a given direction, electrode 14 c can be activated whileelectrodes 14 b, 15 and the conductive wall 17 are connected to the samevoltage (or grounded). This has been found to reduce the NLZ and toincrease potential linearity (prism-like) in each zone 12 and improvebeam steering (or in a circular geometry improve Fresnel lens operationefficiency).

For clarity, connecting electrode 14 b and the conductive wall 17 to thesame voltage can be selectively achieved externally in driver circuit20. An isolation layer (not shown) can be employed between electrodes 14c/14 b and conductive wall 17. For example, the incident light can besteered in the opposite direction by connecting electrodes 14 c, 15 andconductive wall 17 to the same voltage (or grounded) while electrode 14b is activated.

FIG. 7B illustrates another embodiment of the proposed solutionemploying a weakly conductive or highly resistive layer (WCL) 16 in theoptical device geometry illustrated in FIG. 7A. An improved sawtoothprofile can be provided by controlling the frequency of the drive signalcomponents supplied to electrodes 14 b and 14 c. The use of a floatingelectrode 13, in accordance with a further embodiment of the proposedsolution, is illustrated in FIG. 7C, to improve the electric fieldprofile to obtain a more linear prism-like modulation profile. The useof a floating electrode can be used in conjunction with otherembodiments, for example, with embodiments shown in FIGS. 2 to 6.

In accordance with another embodiment of the proposed solution, FIG. 8Aillustrates neighboring zones 12 or beam steering elements 12 of a LCbeam steering device 10 having two stacked LC layers (these layers neednot be immediately adjacent or staggered by a full zone width), in whichcontrol of the electric field is provided by one control electrode(alternating 14 e/14 f) per zone 12 employing wide optically transparentwalls 19 extending in every other inactive element zone 12 in each LClayer however in a staggered pattern between LC layers.

Transparent walls 19 can permit the electric field to penetratetherethrough providing a smooth electric field transition between activeand inactive optical device elements 12 under the active electrode 14 eor 14 f. To steer in a given direction, electrode 14 f can be activatedwhile electrodes 14 e and 15 are connected to the same voltage (orgrounded). To have the same behavior in both the top and the bottomcells, the geometry of the electric field and the alignment directioncan be the same as shown in FIG. 8A.

The arrangement of FIG. 8A has been found to essentially eliminate thefringing field induced undesired reorientation of LC under the activeelectrode 14 f in each zone 12 (since there is no LC in that area) andthus to improve phase delay operation. The incident light can be steeredin the opposite direction by connecting electrodes 14 f and 15 to thesame voltage (or grounded) while electrode 14 e is activated. Each LClayer operates with half the number of active optical device elements 12while light incident on each inactive optical device element 12 in oneLC layer is steered by a corresponding active optical device element 12in the other LC layer.

FIG. 8B illustrates another embodiment of the proposed solutionemploying a WCL 16 in the optical device geometry illustrated in FIG.8A. An improved sawtooth profile can be provided by controlling thefrequency of the drive signal components supplied to electrodes 14 e and14 f. The use of a floating electrode 13 for each active element zone12, in accordance with a further embodiment of the proposed solution, isillustrated in FIG. 8C, to improve the electric field profile to obtaina more linear prism-like modulation profile in each element zone 12.

In accordance with another embodiment of the proposed solution, FIG. 9Aillustrates neighboring zones 12 or beam steering elements 12 of a dualLC layer beam steering device 10 employing staggered wide opticallytransparent walls 19 extending in every other inactive element zone 12in each LC layer, in which control of the electric field is provided byone control electrode (alternating 14 e/14 f) per zone 12. In theembodiments of FIGS. 8A, 8B and 8C, there exists the possibility forlight steered by the front LC layer to be steered again by the back LClayer thereby representing a different cause affecting the NLZ. This hasbeen found to decrease light output in each zone 12. In order todecrease losses due to this resteering and improve phase delayoperation, the central substrate 11 b is omitted in the optical devicelayered geometry. During wafer level manufacture, electrode layer 15(and associated alignment layers) is deposited on each transparent wall19. Flip-chip fabrication techniques can be employed to mate thestaggered electrode strips into electrode layer 15 illustrated. The LCmaterial can be dispensed into the active optical device element zones12, for example by vacuum, injection or capillary action.

FIG. 9B illustrates another embodiment of the proposed solutionemploying a WCL 16 in the optical device geometry illustrated in FIG.9A. An improved sawtooth profile can be provided by controlling thefrequency of the drive signal components supplied to electrodes 14 e and14 f. The use of a floating electrode 13 for each active element zone12, in accordance with a further embodiment of the proposed solution, isillustrated in FIG. 9C, to improve the electric field profile to obtaina more linear prism-like modulation profile in each element zone 12.

In accordance with another embodiment of the proposed solution, FIG. 10Aillustrates a single zone or beam steering element 12 of a LC beamsteering device 10 having two active electrodes 14 e and 14 f each ofwhich are driven by corresponding drive signal components each having anamplitude, frequency and phase. The resulting potential profile acrossthe zone element 12 is cambered as illustrated by the dashed line, forexample by employing a 5V drive signal on 14 e and 14 f (same phase andsame frequency) with respect to electrode 15. In this state the elementzone 12 does not provide beam steering. For reference, unconnectedelectrode 14 c is illustrated to confirm that shaping the potentialprofile in accordance with this embodiment is possible in other opticaldevice geometries without departing from the proposed solution.

FIG. 10B illustrates the two active electrodes 14 e and 14 f of FIG. 10Abeing driven by corresponding drive signal components of same frequencyand amplitudes, but in opposing phases. Beam steering can be provided bydriving electrode 14 e at 5V and electrode 14 f at −5V wherein thepotential profile of the electric field causes the orientation of the LCmolecules to have inflection point in the middle of the zone element 12.FIG. 10C illustrates the two active electrodes 14 e and 14 f of FIG. 10Abeing driven by corresponding drive signal components of differentfrequencies, phase and amplitudes. When the frequency is the same andthere is a phase shift, such as 180 degrees, then there is a substantialelectric field component between the electrodes and thus extending alongan extent of the liquid crystal layer. When the frequency of the drivesignals is different, then the voltage between the electrodes 14 e and14 f is an alternating voltage with a beat frequency, and this voltageprovides an electric field along an extent of the liquid crystal layer.Beam steering can be varied by driving electrode 14 f at 5V andelectrode 14 e at −2V wherein the potential profile of the electricfield causes the orientation of the LC molecules to move the inflectionpoint from the center to one side of the zone element 12.

In-Plane Field Control

Beam control devices are optical devices that control a beam of lighteither with respect to the beam divergence or convergence or withrespect to the beam direction, namely for beam steering purposes.

In the case of liquid crystal devices, an electric field is typicallyused to control an orientation of the liquid crystal material. Thechange in orientation affects the index of refraction and can createwhat is known as a gradient index (GRIN) lens. For beam control, afocusing lens may not be required.

When the aperture of the device is large, beam steering at large anglesis difficult with a liquid crystal GRIN device due to relatively smallvariations in the index of refraction over the aperture. By using anumber of beam control elements over the aperture, smaller opticalelements with a smaller aspect ratio can provide for greater beamsteering ability.

The electric field can be spatially modulated over the aperture of aliquid crystal optical device to spatially modulate the liquid crystalorientation. For lenses, it can be desirable to have a smooth variationof orientation control over the aperture, without using a number of lenselements to form a lens. In the case of beam control devices, the use ofa number of elements can be desirable as mentioned above, and theprofile of the electric field over the small aperture area of eachelement and its interaction with the liquid crystal can be differentfrom larger aperture devices.

In some beam control devices, the controlling electric field is providedusing electrodes arranged on opposed sides of the liquid crystal layer,and in others, the electric field is provided by electrodes arranged onone substrate (11 a/11 b) containing the liquid crystal layer.

Nematic liquid crystal when oriented using a rubbed alignment layer canaffect only one polarization of incident unpolarized light. To modulateunpolarized light, two, orthogonally oriented layers of liquid crystalare commonly used. The first layer causes the light to be split into twoorthogonal polarizations, only one of the polarizations having beenmodulated in accordance with the liquid crystal spatial modulation,while the other polarization is essentially unmodulated. The secondlayer is arranged to provide the desired complementary modulation on thepolarization that was unmodulated by the first layer, and lets themodulated polarization from the first layer pass through with littlemodulation.

For beam steering purposes, it is possible to use a first liquid crystallayer to controllably steer light of one polarization in one direction,while a second liquid crystal layer is used to controllably steer lightof the other polarization in an orthogonal direction.

This can be better understood with reference to FIG. 11 whichillustrates schematically a device having a single liquid crystal layer120 that has interconnected, parallel strip electrodes 114 on onesubstrate 111 separated by an electrode gap g with a transparent planarelectrode 115 arranged on another opposed substrate 111 to provide acontrol electric field across the liquid crystal layer having athickness L (this thickness is sometimes known as the cell gap). Thestrip electrodes 114 can also be transparent even if they are typicallyonly 10 to 20 microns wide and would not block much light transmission.An alignment layer 118 of a rubbed polymer is provided over the internalsurfaces of both substrates 111 to provide an initial ground stateorientation to the liquid crystal 120. The strip electrodes 114 arepreferably provided on the substrate side from which light enters thecell, although they can also be provided on the opposed substrate 111.

The device 100 illustrated schematically and not to scale shows incross-section four electrode gaps each providing a controllablecylindrical lens element for beam control. The arrangement of electrodes114 can be linear (i.e. fingers), concentric rings, a spiral or anyother geometric configuration. The number of electrode gaps over a beamaperture can vary according to the application.

When a voltage is applied across electrodes 114 and 115 in FIG. 11 (seethe field lines illustrated on the right cell), the electric field isstronger in the space below the electrodes 114 and 115 than over thegaps between the electrodes. A layer of a highly resistive material canbe added near the electrodes 114 to help distribute the electric fieldover the gap, however when the aspect ratio of the gap to liquid crystallayer thickness is relatively small, then such a highly resistivematerial layer may not be of much benefit.

A layer of nematic liquid crystal material 120 controls a singlepolarization of light. As is known in the art, such layers can bestacked together so that the device can module both linear polarizationsof light. In the embodiment of FIG. 11, the liquid crystal material 120is shown to have an alignment almost parallel with the substrate suchthat its ground state would have a low pre-tilt angle from left toright. To modulate the orthogonal polarization, another layer of nematicliquid crystal can be provided to have an alignment parallel with thesubstrate extending into or out of the page. In this configuration, atransparent (and preferably optically matched) filler 122 of desireddimensions is provided to separate the liquid crystal or the electricfield of neighboring cells. A first controllable voltage source V1 isconnected across strip electrodes 114A and an opposed planar electrode115, and a second controllable voltage source V2 is connected acrosselectrodes 114B and the opposed planar electrode 115. The voltages V1and V2 determine the liquid crystal orientation and thus the directionof tilt of the beam steering. The filler can be any suitable material,preferably a transparent material, and also preferably one having anindex of refraction similar to the liquid crystal material. In contrast,the separation of electric fields of neighboring cells will be possibleonly if the filler 122 is conductive and controlled. The phase delayprofile of the liquid crystal between two fillers 122 can have adesirable beam steering quality.

Furthermore, for beam control purposes, the strip electrode patternshown in FIG. 11 can be used to cause beam steering in one directiononly. For beam steering in two directions, additional layers can be usedwith a pattern of control electrodes 114 that are orthogonal.

Similar to FIG. 11, FIG. 12 shows a device having a single liquidcrystal layer 120 that has, on one substrate 111, independent electrodes114A and 1148 separated by a gap to provide a control electric fieldbetween the electrodes that is spatially variable in the liquid crystalbelow the gap. When a voltage is applied across electrodes 114A and 114Bin FIG. 12 (see the field lines illustrated on the two cells on theright), the electric field follows a geometry that is essentially in adirection parallel to the direction between the electrodes at a midpointof the gap, while it turns to be essentially perpendicular to thedirection between the electrodes at the edge of the gap where there isno filler 122. The control field has a very different geometry than thatof FIG. 11, however the liquid crystal orientation under conditions ofthe applied voltage is similar (but not identical). In this embodiment,the transparent material 122 does not respond to the electric field andis provided such that the beam steering index of refraction profile canbe provided with the liquid crystal 120 cells and the transparentmaterial 122 being arranged in a staggered manner on two layers. Thiswill provide a “left or right” tilting capacity of a single polarizationof light in the plane of the drawing.

The embodiment of FIG. 12 has the disadvantage over the embodiment ofFIG. 11 that it can only control steering in one direction. To steer inthe other direction, one would use either separate cells for thatpurpose, or alternatively, if a dual frequency liquid crystal is used,then a higher frequency above the cross-over frequency can be used tocause a liquid crystal alignment orthogonal to the electric field, andthus provide the desired profile for steering in the other direction.

In FIG. 12, the aspect ratio (R) of the spacing (g) between theelectrodes 114A and 114B and the thickness of the liquid crystal layer(L), R=g/L, can be, for example, between 0.7 and 4 (preferably about 2.5for a microlens application) without using any weakly conductive coatingon or at the insulating substrate 111 on which the electrodes 114A and114B are located. For example, g can be about 100 microns, while L canbe about 50 microns for an aspect ratio of about 2. This aspect ratioplays an important role in determining the desired electric fieldspatial variation as described above. The electrodes 114A and 114B areshown arranged on a cell inside side of the substrate 111, however, theycan also be located on an outside side of the substrate 111. This latterarrangement may require a higher drive signal voltage, however, theelectric field geometry can be more suitable for modulating the electricfield within the liquid crystal material.

FIGS. 13A to 13C illustrate schematically in greater detail the electricfield generated from a single pair of parallel strip electrodes 114A and114B similar to those of FIG. 12. FIG. 13A illustrates an aspect ratioof about 5. The electric field lines in the cell are mostly parallel tothe substrate except for fringe areas near the electrodes. Thisarrangement is known for use in displays where the liquid crystal needsto switch between two states, namely a ground state (e.g. twistednematic or homeotropic) and a powered state in which the liquid crystalis aligned parallel to the substrates. In this case, the purpose is toachieve a uniform reorientation of the liquid crystal within the cell(between the electrodes 114A and 114B).

FIG. 13B illustrates a cell geometry in which the aspect ratio R is lessthan about 1. Such an aspect ratio can provide an intensity distributionas a function of viewing angle with side-lobe peaks that are notsuitable for beam steering.

FIG. 13C illustrates a cell geometry in which the aspect ratio R isgreater than about 1 and less than about 4. This geometry provides goodbeam steering performance.

In the embodiment of FIGS. 12 and 13C, the electric field has componentsthat are “vertical” (called “out of plane”), namely perpendicular to thesubstrate at which the electrodes 114A and 114B are located, and“horizontal”, namely extending between the electrodes.

When the liquid crystal is oriented in its ground state by an alignmentlayer 118 that extends in the direction between the electrodes 114A and114B (perpendicular to the electrode strips), the steered beam intensityprofile can be altered due to the asymmetric difference in the anglebetween the electric field and the desired spatial distribution oforientation of the liquid crystal in the cell. As illustrated in FIG.13C, the left side orientation of liquid crystal 120 a is aligned withthe electric field, while the right side orientation of any liquidcrystal (at 120 b) in the filler 122 would be orthogonal to the electricfield.

As will be appreciated from FIGS. 13A, 13B and 13C, the aspect ratio hasan impact on the spatial profile of the liquid crystal orientationwithin the cell, and an appropriate beam shaping optical device can beprovided with a suitable aspect ratio as illustrated in FIG. 13C,whereas FIGS. 13A and 13C provide beam shaping that is not uniform ornot effective.

The strip electrodes 114A and 114B can be narrow enough so as to reducethe size of the boundary zone between adjacent cells. The aperture of adevice having a cell illustrated in FIG. 13C can have many such cells,whether arranged in strips, rings, spirals or other geometric patterns,given the small gap of each cell of about 30 microns to about 90microns, and typically around 50 microns, namely about 20 cells perlinear millimeter of aperture.

The configuration of FIGS. 11 and 12 provides devices that provide nolight modulation under conditions of zero power, and then provide beamcontrol when powered.

In FIG. 14, an alternate configuration is schematically shown in planview in which the direction of the alignment layer is almost in thedirection of the strip electrodes 114A and 114B. Here, the electricfield component in the horizontal or X direction would act on themolecules to turn them sideways against the action of the alignmentlayer. However, the vertical or Z direction component of the electricfield acts on the liquid crystal molecules with good symmetry across thegap. This configuration provides good phase delay profile for beamsteering.

In FIG. 15A, a different electric field arrangement is illustrated thatcan be used for beam shaping and beam steering. In this arrangement, twoLC 120 cells are used to steer (manipulate) a light beam with extraordinary polarization in the drawing plane from left to right or viceversa. All LC molecules are oriented in the same plane of the page,although the orientation of the liquid crystal with respect to thedirection of the strip electrodes 114A and 114B can be chosen forexample to be parallel with the direction of the electrodes as describedabove with respect to other embodiments.

For steering operation, the electrodes 114C are grounded (namelyconnected to ground or an opposite polarity of the drive signal source).There is a voltage provided on electrodes 114A, while the electrodes114B are floating or disconnected. Thus, for steering in one direction,electrodes 114A and 114C can be connected to, for example, analternating current voltage source, while electrodes 1148 aredisconnected. In this case, approximately half of light propagating inthe vertical direction will be steered to the right thanks to the cellsin the upper layer and the other half of light will be steered in thesame direction thanks to the cells in the lower layer. Making theelectrodes 114A floating and the electrodes 1148 connected to a voltagewould allow the steering to the left (for a liquid crystal with positivedielectric and optical anisotropies). The two middle substrates 111between the two liquid crystal layers 120 can be provided as a singlesubstrate 111.

The electric field between the electrodes 114A or 114B and the groundedelectrode 114C are essentially “vertical”, namely perpendicular to thelateral extent of the liquid crystal layer, even if the electrodes 114Aand 114B are somewhat spaced to one side of electrodes 114C. This isillustrated in FIG. 16.

It will be appreciated that the electric field will extend between apowered electrode, for example 114B, and the nearest grounded middleelectrode 114C, the grounded electrode 114C on the opposite side of themiddle substrate 111 and the farther grounded electrode 114C on the sameside of the middle substrate 111. The field strength can be high enoughwhen extending to the closest middle electrode 114C to orient the liquidcrystal 120, while the field strength extending to the fartherelectrodes 114C can be weak enough so as to cause negligible orientationof the liquid crystal 120. Accordingly, such field lines are suitablefor orienting liquid crystal 120 having a ground state orientation(provided by alignment layers) that is close to the substrate planes111, as illustrated. The electric field lines are strongest in theregion below the powered electrodes 114A and/or 114B, and are muchweaker in the direction away from the nearest electrode 114C, andlikewise drop off gradually in strength in the direction towards themiddle of the electrodes 114C. This provides for an electric fieldgradient that is suitable for a spatially variable orientation of theliquid crystal material 120 to provide the beam steering or beam shapingelement.

The arrangement of a strip electrode with an opposed offset middleelectrode 114C provides a phase delay profile as illustrated in FIG. 17.The simulation in FIG. 17 was done for a thickness of liquid crystal of50 microns, strip electrode 114 widths of 20 microns, a gap between thestrip electrodes 114A and 114B of 100 microns. The offset, as shown inFIG. 16, does not need to be very much. Considered from the center ofthe beam steering element, the strip electrode 114A or 114B's outsideedge extends about 20 microns from the corresponding outer edge of theoffset middle electrode 114C. This is the width of the strip electrode114A or 114B. The inside edges of the electrodes 114A or 114B may indeedoverlap with the middle electrode 114C, or not (in FIG. 18A, theparameter ‘d’ can be positive, zero or slightly negative, as long asthere is sufficient extension of the strip electrode 114B beyond themiddle electrode 114C). The amount of this offset can vary as desired,the effect being to reduce the fringe electric field outside of theelement 112.

As illustrated in FIG. 15B, the offset can also be the result of themiddle electrode 114C extending farther than the strip electrodes 114Aand 114B. The result is the same, namely the fringing field is reduced,and the desired beam steering phase delay profile can be achieved.

The asymmetry between steering right and steering left might beexplained by a liquid crystal planar orientation that was extendingperpendicularly between the strip electrodes 114A and 114B, and thus theresponse to the electric field would be somewhat asymmetric with theelements.

What is striking about the simulation results of FIG. 17 is the verysteep rise in the phase delay from minimum to maximum, as illustrated bythe reference label B. This results from the reduction in the fringefield as described above due to the offset. As shown, this rise orreturn region represents only about 20% of the aperture. It should alsobe noted that this is achieved by using electrodes on the insidesurfaces of the substrates, so that voltages are lower, and with asingle control signal. The device also avoids the need for any weaklyconductive layer.

The approximately 20% return region of the aperture will scatter ordirect light in the opposite direction. In some applications, thiseffect is acceptable, and in others, it is not. When it is notacceptable, the portion of the beam steering elements where the returnregion is found can be masked. While this reduces the transmissionefficiency of the device, it can remove the scattered or wronglydirected light. As illustrated in FIG. 17, if the combined returnregions for both right and left steering were masked, there would be a60 micron usable steering zone out of the electrode gap of 100 micronsmaking up the steering elements. As mentioned above, if the liquidcrystal alignment were as shown in FIG. 14, one might expect that thesize of the combined return regions would be less due to greatersymmetry between right and left steering modes.

FIG. 18A illustrates an embodiment similar to FIG. 15A in which odd andeven elements have offset middle electrodes 114C and 114D. This deviceis driven by alternatingly applying a drive signal as shown in FIG. 18Aand then as shown in FIG. 18B. Each configuration provides the electricfield for forming beam steering elements in odd or even ones of theelements of the device. By time multiplexing the electrode driveconfigurations, the liquid crystal layer 120 can be provided with beamsteering phase delay profiles in all elements.

Using drive circuitry that comprises electronic switches, a drive signalis first applied across electrodes 114A and 114C (with 114B and 114Dbeing disconnected) for steering in one direction, while applying adrive signal across electrodes 114B and 114C for steering in the otherdirection (with 114A and 114D being disconnected). In FIG. 19, the phasedelay of this first “fingers set activated” is shown. The beam steeringramp is about 80 microns and the return region is about 20 microns.Secondly, the drive signal is applied across electrodes 114B and 114D(with 114A and 114C being disconnected) for steering in one direction,while applying a drive signal across electrodes 114A and 114D forsteering in the other direction (with 114B and 114C being disconnected).In FIG. 19, the phase delay of this second “fingers set activated” isshown (drive voltage is 10V, the liquid crystal material is LC80 and is50 microns thick with electrode period of 120 microns, the electrodes114A and 114B being 20 microns wide). The beam steering ramp and thereturn region characteristics are essentially the same for the twoconfigurations, and there is a small ripple of modulation shown causedby each configuration on the unmodulated elements between the currentlypowered or modulated elements. The drive circuitry switches between thefirst and second configurations back and forth to achieve themaintenance of the beam steering phase delay profiles for all elementsof the device.

In the embodiment of FIG. 18A, it is preferred to use middle electrodes114C that are inset from the opposed strip electrodes as illustrated,since each strip electrode can be used for both left and right beamsteering control. However, following the configuration of FIG. 15B canbe done in the context of FIG. 18A, however the offset then requiresthat separate inset strip electrodes be used for left and right beamsteering, with the electrodes 114C and 114D being separated only by avery small insulating gap. Thus, electrodes 114A and 114B would beprovided as electrodes 114A-right, 114A-left, 114B-right and 114B-left.

The device of FIG. 15A or 18A manipulates one linear polarization oflight in one plane, and can be considered to be a “quarter unit”. Twosuch elements with orthogonal electrode lines, but having the LCmolecules in the same plane can be used to manipulate the samepolarization, but in two planes to form a “half unit”. Furthermore, two“half-units” (overall 8 LC cells) can be provided to manipulateunpolarized light in two planes. A beam steering device that operates intwo planes can move a beam in two orthogonal directions.

A beam controller is provided to generate control signals. For example,the light source, such as the LED die, can be controlled in intensityand/or in color using the beam controller. Also, the dynamic liquidcrystal control element can be controlled using the beam controller,namely the electrodes 114A and 114B (or any of the electrodearrangements described above) can be controlled using the beamcontroller circuit. The beam controller can comprise dedicated circuitryor it can comprise configurable circuitry (e.g. FPGA), or it can beimplemented using program code running on a suitable platform, forexample a CPU or DSP based system.

The beam controller can be configured to receive control commands over adata network to adjust the beam direction. Some light sources, forexample infrared light sources, can be used to provide datacommunication, and in this case the beam controller can be used tomodulate the light source with data, while the dynamic LC controlelement can be used to steer the data-carrying beam. This can be usefulfor scanners, receivers and readers in addition to light projectors orsources.

In the embodiment of FIG. 20, there is shown an electrode array havingstrip electrodes 114A and 114B. The electrode spacing is 50 microns inthe middle of the 6 mm aperture of the device and 100 microns at theouter sides. In the example illustrated, the gap increases/decreases by5 microns from one gap to the next. Small gaps have a higher beamshaping or beam steering ability or power, and larger gaps have smallerpower.

Such variation of strip electrode gap may be linear or non-linear. Aneffect of the variation or chirp can be to eliminate or reduce any colorseparation and hot spot formation in the transmitted light. This isbecause different portions of the optical element will redirect the samewavelength (i.e. color) of light in different directions.

For example, a beam can have symmetry with respect to an optical axis.In such as case, the electrodes can be provided as concentric rings 114Aand 114B (essentially forming a Fresnel lens). The spacing of the ringscan be closer near the central optical axis, and farther apart near theoutermost ring to provide a beam spread that is more even. The spacingcan also take into consideration a beam intensity profile to providemore elements where the intensity is greater. This type of electrode(concentric rings) may be used along with a star-shaped inter-digitatedelectrode structure on the opposed substrate of the cell.

It will be appreciated that strip electrode patterns as described hereincan be applied to a variety of liquid crystal cell designs. In the caseof concentric rings, beam shaping or beam steering is done in the oneradial direction with respect to the optical axis, and thus a typicaldesign might have two layers of liquid crystal, one for eachpolarization. The spatial chirp may also be applied in circular or starshaped electrode cases.

A liquid crystal device 10/110 such as in the above embodimentscomprises LC layers having alignment layers aligned in one direction. Asbriefly mentioned hereinabove, such a device 10/110 acts on a singlelinear polarization of light and unpolarized light passing through thedevice is processed by the optical device as two linear polarizationstates. The spatial modulation of the index of refraction in the LCmaterial provided with respect to the extraordinary polarized light,while the other ordinary polarized light does not experience a spatialmodulation of the index of refraction. In order to control unpolarizedlight, a second optical device 10/110 is typically provided withalignment layers oriented orthogonally to those of the first opticaldevice to act on the other polarization. This is schematicallyillustrated in the FIG. 21, that is electrodes 114 and 115 are providedin respect of an additional LC cell in a manner similar to the first LCcell. It is also known from international patent application publicationWO2009/146530 published 10 Dec. 2009 to arrange four LC cells together,with alignment layers of two LC cells acting on the same lightpolarization having alignment layers oriented in opposite directions asillustrated in FIG. 21. Such an arrangement of four LC cells reduces thesensitivity or image aberrations of the device 10/110 to incident lightthat is not parallel to the optical axis of the overall device as thelight passes through the overall device.

While FIGS. 5 through 20 illustrate a beam steering device, thearrangement used to cause liquid crystal to change orientation acrossthe zone boundary with a reduced non-linear zone can also be used for avariety of Fresnel lens designs, for example as illustrated in FIG. 22.In such cases, the electrode geometry will be different and will notform only rectangular zones, but rather typically arcuate or circularzones, as is known in the design of Fresnel lenses. In the lens shown inFIG. 22, the conventional refractive counterpart lens is illustrated atthe top of the page in dashed lines in cross-section aligned with a fourlayer liquid crystal gradient index lens having a similar behavior. Thecentral zone is created by the central ring electrode 14 c providing incombination with the weak conductive material 16 (not shown in FIG. 21)an axially symmetric voltage distribution in the central area that tendsto zero near the optical axis. In this illustration, the bands aremaintained as the same size as the conventional Fresnel lens, however itwill be understood that the dimensions of each micro element using suchliquid crystal devices will be typically much smaller and more numerousthan would be used when making a Fresnel lens from a thicker opticalrefractive material. The electrodes 14 c and 14 d are shown with greaterseparation than would normally be implemented for ease of illustration.The electrical connections between the electrodes 14 c and 14 d and thedriver signal sources are also not illustrated for ease of illustration.The four layers of liquid crystal material (FIG. 21) have orientationsas illustrated to provide for good optical performance on natural light(both polarizations) and with reduced sensitivity to light that is notparallel to the optical axis. Such a lens 10 can be fully effective withonly two layers to work with natural light if the rays stay close tobeing parallel to the optical axis. Additional layers can also be usedto increase the thickness of the lens material and thus the opticalpower.

The device illustrated schematically in FIG. 6 and as described aboveusing different electric field control structures described withreference to FIGS. 7 to 22 above, or a different Fresnel lens design canbe applied to a variety of applications including redirection of lightemitted by LED light sources for illumination purposes. Liquid crystalmaterials can also be used for steering or focussing infrared light, forexample 850 nm, and a device as described above can be used to scan inthe infrared spectrum.

It will also be appreciated that optical devices can be made accordingto above embodiments that are operative into the terahertz frequency,namely within the wavelength range of 8000 to 14000 nm of human bodyradiation. Thus tunable control over Fresnel refractive lenses and/orthe ability to control beam steering of a projected beam of infraredlight for detectors sensitive to this range of wavelengths can finduseful application, for example, in the optics of infrared motiondetectors.

While the invention has been shown and described with reference topreferred embodiments thereof, it will be recognized by those skilled inthe art that various changes in form and detail may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims.

What is claimed is:
 1. A liquid crystal optical device providing beamsteering multiple refractive or refractive Fresnel lens type elementcontrol over light passing through an aperture, the device comprising: alayer of liquid crystal material contained by substrates havingalignment layers; and an arrangement of electrodes configured to providea spatially varying voltage distribution within a number of microelement zones within said liquid crystal layer; characterized in thatthe liquid crystal optical device is structured to provide a spatialvariation in the optical phase delay with an abrupt transition at aboundary between micro elements that is an approximation of a sawtoothwaveform across the boundaries of multiple micro elements to increasesthe effective aperture of the optical device.
 2. The liquid crystaloptical device as defined in claim 1, further comprising a drivercircuit configured to provide drive signals to said arrangement ofelectrodes.
 3. The liquid crystal optical device as defined in claim 2,wherein the liquid crystal layer comprises dual frequency liquid crystalmaterial, the arrangement of electrodes comprises first and secondelectrodes near a boundary between adjacent ones of said zones, and adrive signal for said first electrode is of a low frequency for causingalignment of the dual frequency liquid crystal material parallel to theelectric field, and a drive signal for said second electrode is of ahigh frequency for causing alignment of the dual frequency liquidcrystal material perpendicular to the electric field.
 4. The device asdefined in claim 1 or 2, wherein said arrangement of electrodes furthercomprise floating electrodes that help to shape the electric fieldwithin the micro elements.
 5. The device as defined in claim 1 or 2,comprising a pair of liquid crystal layers each having micro elementsseparated by optically inert zones unaffected by a variable electricfield, wherein said pair of layers combine to provide a desired opticalcontrol and the optically inert zones allowing for an abrupt change inphase delay between liquid crystal and optically inert zones.
 6. Thedevice as defined in claim 5, wherein the micro elements on one liquidcrystal layer correspond to optically inert zones of the other liquidcrystal layer.
 7. The device as defined in claim 1 or 2, comprising aconductive wall arranged between liquid crystal micro elements, so thatthe electric field acting on the liquid crystal of the micro elementsdoes not act on the liquid crystal of neighboring micro elements.
 8. Thedevice as defined in claim 2, wherein the driver circuit is configuredto provide a potential difference in electrical signals supplied to theelectrodes of the liquid crystal micro elements at one substrate, sothat the electric field acting on the liquid crystal of the microelements is directed in part in a direction of the liquid crystal layerdirection.
 9. The device as defined in claim 8, wherein the drive signalis an AC signal, and the potential difference is provided using a phasedifference in said electrical signals.
 10. The device as defined in anyone of claims 1 to 9, wherein the arrangement of electrodes compriseshole-patterned electrodes.
 11. The device as defined in claim 10,wherein the arrangement of electrodes further comprises a weaklyconductive material for distributing voltage from the electrodes over anaperture of the zones.
 12. The device as defined in any one of claims 1to 9, wherein said arrangement of electrodes comprises: a patternedelectrode structure comprising strip electrodes on one of saidsubstrates and middle electrodes on another of said substratespositioned near a middle of said steering elements and offset from aposition opposite said strip electrodes such that an electric fieldbetween said strip electrodes and said middle electrodes provides astrong field with reduced fringe fields near an offset between saidstrips electrodes and said middle electrodes and a gradually reducingelectric field across said middle electrodes without needing a weaklyconductive material for distributing voltage from the electrodes over anaperture of the zones.
 13. The device as defined in claim 12, whereinsaid strip electrodes are arranged near each side of said middleelectrodes for selectively steering light in different directions byselectively driving ones of said strip electrodes on a chosen side ofsaid middle electrodes.
 14. The device as defined in claim 13, whereinsaid middle electrodes are inset between said strip electrodes.
 15. Thedevice as defined in claim 13, wherein said strip electrodes are insetbetween said middle electrodes.
 16. The device as defined in any one ofclaims 12 to 15, wherein said device comprises two said liquid crystalcells, a first one of said two cells providing odd beam steeringelements separated by inactive elements and a second one of said twocells providing even beam steering elements separated by inactiveelements, said odd beam steering elements being aligned with saidinactive elements separating said even beam steering elements.
 17. Thedevice as defined in any one of claims 12 to 15, wherein said middleelectrodes are provided for each of said beam steering elements arrangednext to one another, said middle electrodes able to be driven in analternating manner to maintain said beam steering spatial pattern. 18.The device as defined in any one of claims 1 to 17, wherein arrangementof electrodes has a linear pattern.
 19. The device as defined in any oneof claims 1 to 17, wherein arrangement of electrodes has a spiral orcircular pattern.
 20. The device as defined in any one of claims 1 to19, wherein said micro element zones have a variation in width over anaperture of the device.
 21. The device as defined in any one of claims 1to 20, further comprising a drive signal controller for generating atleast one drive signal for said arrangement of electrodes.
 22. Thedevice as defined in any one of claims 12 to 20, further comprising adrive signal controller for generating at least one drive signal forsaid arrangement of electrodes, wherein said drive signal controller isconfigured to selectively connect some of said electrodes to a drivesignal and disconnect others of said electrodes to be floating.
 23. Thedevice as defined in claim 22, wherein said drive signal controller isconfigured to drive said device in a beam broadening mode.
 24. Thedevice as defined in claim 22 or 23, wherein said drive signalcontroller is configured to alternatingly connect different groups ofsaid electrodes corresponding to different groups of said plurality ofbeam steering elements to a drive signal and disconnect others of saidelectrodes to be floating.
 25. The device as defined in any one ofclaims 1 to 24, wherein said beam steering device is configured to steerlight in two orthogonal planes.
 26. The device as defined in any one ofclaims 1 to 25, wherein the device is a Fresnel lens, and thearrangement of electrodes comprises strip electrodes defining boundariesbetween Fresnel micro elements.
 27. The device as defined in any one ofclaims 1 to 26, comprising two said layers of liquid crystal close toeach other and arranged with liquid crystal orientations orthogonallybetween the two layers.
 28. The device as defined in any one of claims 1to 26, comprising four said layers of liquid crystal close to each otherand arranged with liquid crystal orientations orthogonally and inopposed directions among the four layers.